1. Field of the Invention
This invention relates to safety mechanisms for cable drums, and more particularly, to a system for indicating drive train failure between a prime mover and cable drum by comparing the revolutions of the prime mover to that of the cable drum.
2. Description of the Prior Art
Mechanical systems such as winches and cranes utilizing flexible cables wrapped around cylindrical cable drums are well known and in common use. Such cable drums are generally driven by a high speed prime mover, such as an electric drive motor, through a speed reducing drive train composed primarily of interlocking gears. Although these drive trains are extremely reliable, the consequences of a drive train failure are extremely severe since a failure could allow a heavy load to fall freely. Consequently, it is important to be able to detect such drive train failure and automatically terminate cable drum rotation before the load connected to the cable has fallen sufficiently to build up significant momentum. Furthermore, the operation of the safety system should not depend upon other systems, such as the mechanism's electrical system, since a drive train failure may also be accompanied by an electrical failure.